No, forests are not the lungs of the worlds, the oceans are. I'm not sure about that "per area" production, but in total oceans are much more important (as they constitute 70% of the Earths surface). But still, what hasn't been said probably yet, forests are very important for the ecology ...

As you must be able to grow the bacteria (otherwise you cannot perform the test at all), it would be better to perform dilution of your samples and spread aliquots of such on plates with growth agar (for E.coli simple LB, for Kefir, no idea). Let them growth (E.coli for 1 day at 37°C) and count numb...

@sosippus just two things1) how would they detect the luminiscence? Better would be some chemical signal as we know it from here.2) surprise, surprise, bacteria do not require organic carbon sourcehttp://en.wikipedia.org/wiki/Autotroph

Well, I'd say that usually the floor is probably not considered as really clean. It's not like the bacteria would actually climb up, but if you spill them, they will spread. But the floor thing is probably rather to protect your sample from contamination, not the other way. You do have bacteria on y...